1. Technical Field
This invention relates generally to optical display devices, and more particularly to an optical device, such as a substrate guided relay, that employs a light homogenization device at its input and that is configured to transfer light from a source to a user's eye.
2. Background Art
Substrate guided relays are devices that transmit light rays from a source to a viewer. Generally, substrate guided relays are optical image transfer devices that include a substrate, which may manufactured from glass or fused silica, and which directs light from a relay input to a relay output. This light can be guided along its path by the optical transfer properties of the substrate. These optical transfer properties can additionally work in tandem with reflective or diffractive devices coupled to the substrate. The surfaces of the substrate can also work to direct the light to its intended destination. In many applications, this end destination is a viewing region that is directed to a projection surface or a user's eye. One application of substrate guided relays is that of a near-to-eye display in which the viewing region projects directly into the pupil of a user.
Substrate guided relays generally include three basic components: an input that collects and receives light from a source, a substrate that transfers the light, and an output that delivers light away from the substrate. In many applications, it is advantageous to keep the various components of the substrate guided relay assembly small, as they are sometimes used as head mounted displays or other compact display systems. This desire to keep size to a minimum creates challenges, however, for the designer. In particular, when a source of light is small, the light often has a smaller spatial extent. It can therefore be challenging for a substrate guided relay designer to create a display having a pupil that is much larger than the extent of the source.
When large projection sources are used, the image pupil is often on the order of the original image and little or no pupil expansion may be required. Where required, the expansion may be needed in only one direction. When the projection source becomes smaller, however, the pupil becomes smaller. To create a uniformly bright image, a great deal of pupil expansion must occur. Some scanned beam light sources producing narrower input beams do not generate sufficient pupil sizes for uniform images in traditional substrate guided relays. Further, field of view and image size can also be limited when small light sources are used.
There is thus a need for an improved substrate guided relay capable of expanding the pupil and enhancing output uniformity that is compatible with compact, scanned light sources.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.